We are pursuing an in-depth investigation on the structure and function of the membrane receptor for immunoglobulin E (IgE). The principal cells with which we are working is a line of rat basophilic leukemia cells which can be grown in vivo as solid tumors or in vitro. Recent findings include 1) The discovery and characterization of a pair of previously unrecognized subunits so that the receptor is now thought to consist of an alpha, a beta and two gamma chains, 2) A novel in vitro phenomenon whereby the beta and gamma chains become disulfide cross-linked during immunoprecipitation - a phenomenon that could have an important in vivo counterpart, 3) Demonstration that the beta and gamma chains anchor the alpha chains into the membrane, 4) Changes in the state of phosphorylation of both beta and gamma chains as a consequence of triggering the cells and 5) Demonstration that the initial perturbations associated with receptor-mediated triggering can be monitored by a probe sensitive to the plasma membrane potential.